The present invention relates to an offset printer, and more particularly, to a multiple color offset printer in which a surface of a plate cylinder is divided into a plurality of regions to which inks of different colors are supplied.
Japanese Patent Application Publication No.9-510410 discloses an offset printer capable of performing offset printing with four different colors of inks. The printer includes a single impression cylinder, a single paper discharge mechanism, a single paper feed conveyer, a single transfer drum, two blanket cylinders, two plate cylinders and, ink rollers for the four colors. The paper feed conveyer and the transfer drum are adapted for delivering a paper to a surface of the impression cylinder. The paper is mounted on the surface of the impression cylinder. The paper discharge mechanism is adapted to discharge the paper from the impression cylinder. The blanket cylinder is pressed against the paper mounted on the impression cylinder.
The impression cylinder is rotated about its axis by a drive motor. Further, two blanket cylinders have their axes extending in a direction parallel with the axis of the impression cylinder, and the two blanket cylinders are in contact with the impression cylinder and are rotated upon rotation of the impression cylinder. The paper feed conveyer, the transfer drum and the paper discharge mechanism are also driven or rotated by the rotation of the impression cylinder.
Each plate cylinder has a peripheral surface provided with a thin plate where an image to be printed is formed. The two plate cylinders have their axes extending in a direction parallel with the axes of the blanket cylinders. Each plate cylinder is in contact with each blanket cylinder, and each plate cylinder is rotated upon rotation of each blanket cylinder. Each peripheral surface of the plate cylinder is divided into first and second regions. The first region is formed with an image with a single color of ink, and the second region is formed with an image with a different color of ink. Accordingly, the two plate cylinders form images of four colors of inks.
The ink roller is adapted for supplying an ink to the plate of the plate cylinder. To this effect, two ink rollers are provided in contact with each plate cylinder so that two different colored inks can be supplied to each plate. Accordingly, totally four ink rollers are provided for four different colors. Axes of the ink rollers extend in parallel with the axis of the plate cylinder. The ink rollers are rotated upon rotation of the plate cylinder.
If an intended color of ink is to be supplied to the first region on the surface of the plate cylinder, the plate cylinder and the ink roller of this color are rotated with the ink roller being in contact with the first region. During the rotation, the intended color is supplied from the ink roller to the first region.
In the conventional offset printer, a mechanism for accurately moving the ink roller into contact with or out of contact from the specific region on the surface of the plate cylinder has not been proposed. That is, no detailed arrangement or mechanism is proposed for bringing the ink roller into contact with the first plate region when the first plate region is circularly moved closed to or toward the ink roller carrying the intended ink color in accordance with the rotation of the plate cylinder, and for moving the ink roller away from the second plate region when the second plate region is circularly moved closed to the ink roller in accordance with further rotation of the plate cylinder.
It is therefore, an object of the present invention to provide an offset printer provided with a moving mechanism capable of bringing the ink roller provided in a predetermined ink supplying mechanism into contact with a specific plate region on the surface of the plate cylinder, and capable of moving the ink roller away from the different plate region on the surface of the identical plate cylinder.
This and other objects of the present invention will be attained by an offset printer including a frame, a plate cylinder, a plurality of ink supply units, and a moving mechanism. The plate cylinder is rotatably supported by the frame and has an outer peripheral surface sectioned into at least two plate segments extending between ends of the plate cylinder. Each of the ink supply units supplies a different colored ink. The ink supply units are provided in one-to-one correspondence with the plate segments, and each ink supply unit includes an ink roller contactable with its corresponding plate segment so that the at least two plate segments receive inks of different colors. The moving mechanism is provided for each ink supply unit and is supported on the frame and is connected to the ink roller of each ink supply unit for moving the ink roller into contact with the corresponding plate segment and for moving the ink roller out of contact from each non corresponding plate segment.
With this arrangement, a predetermined color of ink can surely be supplied to only a predetermined plate segment, and the supply of the predetermined color of ink to unwanted plate segment can surely be avoided.
Preferably, means for restraining excessive contacting pressure of the ink roller against the plate cylinder is provided. Further preferably, means for adjusting contacting pressure of the ink roller against the plate cylinder can be provided. Thus, a desirable contacting pressure can be provided.
Further, in the present invention, each ink supply unit includes at least two ink rollers including a first ink roller and a second ink roller, and preferably, the moving means includes different timing means for providing an out of contacting timing of the first ink roller from the corresponding plate segment different from an out of contact timing of the second ink roller from the corresponding plate segment, and for providing a contacting timing of the first ink roller with the corresponding plate segment different from a contact timing of the second ink roller with the corresponding plate segment.
With such an arrangement, each ink roller can be brought into contact with the plate cylinder when a leading edge of the corresponding plate segment reaches each ink roller, and can be moved out of contact from the plate cylinder when a trailing end of the corresponding plate segment reaches each ink roller. Accordingly, the corresponding plate segment can provide a uniform ink density over its entire area.
Further, the at least two plate segments preferably include a first plate segment having a semi-circular cross-section and a second plate segment having a remaining semi-circular cross-section, and the moving means further includes a first support arm, a second support arm, and the different timing means includes a first cam member, a second cam member and a generally circular center cam. The first support arm is pivotally movably supported on the frame and rotatably supports the first ink roller. Pivotal movement of the first support arm moves the first ink roller into contact with and out of contact from the plate cylinder. The second support arm is positioned spaced away from the first support arm in a circumferential direction of the plate cylinder. The second support arm is pivotally movably supported on the frame and rotatably supports the second ink roller. Pivotal movement of the second support arm moves the second ink roller into contact with and out of contact from the plate cylinder. The first cam member is pivotally movably supported on the frame and has one end contactable with the first support arm and another end provided with a first cam follower. Pivotal movement of the first cam member pivotally moves the first support arm. The second cam member is pivotally movably supported on the frame and has one end contactable with the second support arm and another end provided with a second cam follower. Pivotal movement of the second cam member pivotally moves the second support arm. The generally circular center cam is disposed coaxially with the plate cylinder and is positioned therebeside. The circular center cam includes a first radius cam face provided at a rotation phase equal to the first plate segment, and a second radius cam face having a radius different from the first radius and provided at a rotation phase equal to the second plate segment. The first and second cam followers are in successive rolling contact with the first radius cam face for successively contacting the first and second ink rollers with the first plate segment, and the first and second cam followers are in successive rolling contact with the second radius cam face for successively moving the first and second ink rollers out of contact from the second plate segment.
With this arrangement, contacting and out of contacting movement of the ink rollers relative to the plate cylinder can be determined by the generally circular center cam rotatable together with the plate cylinder. Therefore, accurate movement of the ink rollers results.
Further, preferably, each ink supply unit includes a plurality of ink rollers, and the offset printer further includes an interlocking mechanism for simultaneously moving the plurality of ink rollers out of contact from the corresponding plate segment in case of a stop of supply of ink to the corresponding plate segment, and for simultaneously moving the plurality of ink rollers toward the corresponding plate segment.
With this arrangement, the plurality of ink rollers can be simultaneously moved out of contact from the plate cylinder by the interlocking mechanism if ink supply to the plate cylinder is to be stopped. Therefore, it is unnecessary to provide an additional arrangement for driving the ink rollers to move out of contact from the plate cylinder. Thus, a resultant offset printer can provide a simple arrangement with the reduced mechanical parts.